While conventional brush-commutated DC motors may have numerous advantageous characteristics such as convenience of changing operational speeds and direction of rotation, it is believed that there may be disadvantages, such as brush wear, electrical noise, and radio frequency interference caused by sparking between the brushes and the segmented commutator, that may limit the applicability of such brush-commutated DC motors in some fields such as the domestic appliance field including the laundry apparatus field. Electronically commutated motors, such as brushless DC motors and permanent magnet motors with electronic commutation, have now been developed and generally are believed to have the abovediscussed advantageous characteristics of the brush-commutated DC motors without many of the disadvantages thereof while also having other important advantages. Such electronically commutated motors are disclosed in the David M. Erdman U.S. Pat. Nos. 4,005,347 and 4,169,990 and Floyd H. Wright U.S. Pat. No. 4,162,435, all of which are commonly assigned with the present application and are hereby incorporated by reference. These electronically commutated motors may be advantageously employed in many different fields or motor applications among which are domestic appliances, e.g., automatic washing or laundry machines such as disclosed in commonly assigned, co-pending U.S. patent application Ser. No. 412,421 filed Aug. 27, 1982, now U.S. Pat. No. 4,449,079; Ser. No. 367,951 filed Apr. 13, 1982, now U.S. Pat. No. 4,528,485; Ser. No. 400,319 filed Sept. 25, 1980, now U.S. Pat. No. 4,459,519; Ser. No. 141,268 filed Apr. 17, 1980, now U.S. Pat. No. 4,390,826; Ser. No. 77,784 filed Sept. 21, 1979, now U.S. Pat. No. 4,327,302; and Ser. No. 463,147 filed Feb. 2, 1983.
Laundry machines as disclosed in the above patent applications are believed to have many significant advantages over the prior art laundry machines which employ various types of transmissions and mechanisms to convert rotary motion into oscillatory motion to selectively actuate the machine in its agitation washing mode and in its spin extraction mode. Such prior art laundry machines are believed to be more costly and more complicated to manufacture, consume more energy, and require more servicing. Laundry machines with electronically commutated motors require no mechanical means, other than mere speed reducing means, to effect oscillatory action of the agitator or tumbler, and in some applications, it is believed that the spin basket might be directly driven by such a motor. While the past control systems, such as those disclosed in the aforementioned coassigned applications for instance, undoubtedly illustrated many features, it is believed that the control systems for electronically commutated motors in general, and for such motors utilized in laundry machines, could be improved, as well as the methods of control utilized therein.
In some of the known control systems, the position of the rotatable assembly (i.e., the rotor) of the electronically commutated motor was located by sensing the back emf of one of the winding stages on the stationary assembly (i.e., the stator) thereof. More particularly the back emf of an unenergized winding stage was sensed and integrated to determine rotor position during any one commutation period in a sequence of commutation. With the advent of inexpensive microprocessor chips, controlling an electronically commutated motor with a microprocessor and discrete element control system has been described. Coassigned U.S. Pat. No. 4,250,544, "Combination Microprocessor and Discrete Element Control System for a Clock Rate Controlled Electronically Commutated Motor" issued Feb. 10, 1981, to R. P. Alley discloses such an arrangement and is hereby incorporated by reference. It is believed that further improvements and other departures can be made in methods and systems for controlling electronically commutated motors and for domestic appliance applications including laundering apparatus applications.